1. Field of the Invention
This invention relates to new and improved single and multigroove sheet metal pulleys such as are used in automobiles and similar and related applications. This invention also relates to a new and improved method and apparatus for forming the grooves in such new and improved single and multigroove sheet metal pulleys from a cup-shaped blank in a single, continuous step without handling, displacement or relocation of the blank during formation of the pulley grooves.
More particularly, this invention relates to a new method or process for forming the grooves in new and improved single and multigroove pulleys, in which the groove(s) are formed and at least one wall of a groove is shaped, folded double or crimped, in a single step from a drawn blank, by the use of external, mechanical force and internal fluid of selectively adjustable volume and pressure, sequentially controlled so that external pressure and motion is exerted on the blank during groove formation and the changing volume and pressure and support, within the blank, together with the location, sizing and closing of the spacing surrounding the blank determine the position and size of the grooves, respectively, and the flow and working of the metal of the blank by and from which the grooves are formed, and wherein the external mechanical force (pressure) applied axially is markedly greater than the applied internal force or pressure which need only be sufficient to prevent internal displacement of the wall or metal during bulging.
2. Description of the Prior Art
Numerous apparatus and processes have been proposed for forming sheet metal pulleys from a single, hollow blank by a plurality of steps depending primarily on the application of an axial force and/or an internal radial force to the blank to force the wall to bulge or flow outwardly, in which the internal force of pressure was of the same or greater order than the axial force and was applied by means of either a deformable, compressible mass or a liquid of adjustable volume disposed within the blank and adapted to fill the interior thereof in accordance with the objectives of the particular apparatus or process.
One of the apparatus and methods which has enjoyed some commercial success and has been used to provide original equipment pulleys for automobiles, and the like, is based upon the disclosures found, for example, in U.S. Pat. Nos. 2,493,053; 2,929,345 and 3,124,090. Briefly, this process comprises stamping and drawing a piece of sheet metal to form a cup-shaped blank having an external flange at the open end and distorting the blank, by means of axial and radial or lateral pressure exerted by compacting a deformable rubber mass, to displace or bulge the adjacent portion of the blank outwardly and then, as a separate step, after the rubber mass has regained its original shape and been removed, upsetting or exerting an axial pressure on said blank, to bend or collapse said bulge into a compact flange. Additional flanges and grooves were formed in the same way with the blank being moved or relocated to a different press for the formation of each separate groove (flange). Sizing and finishing were accomplished on still other apparatus including appropriate sizing rolls after the grooves were formed by the multistep process just described.
While, as noted, this process enjoyed some commercial success, it has nevertheless proven expensive, inefficient and difficult in actual use and has, therefore, been abandoned in whole or in part, as not commercially feasible and practical. This was because of (a) the large number of separate steps actually used in the process; (b) the great amount of handling, moving and relocating of the blank which was necessary during groove (flange) formation; (c) the difficulty in obtaining exact repeatability as to the groove and flange structure in successive pulleys through use of the process; (d) the relatively high cost of the rubber, both initially and as a replacement cost, because of the excessive wear to which the same was subjected; (e) the inability to form symmetrical, properly balanced pulleys in a sufficiently high percentage of instances, with consequent economic loss by rejection or additional manufacturing cost to reform, correct and balance the pulleys.
Other pulleys for the same purpose have been formed by a spinning or rolling process in which expandable roller mandrels disposed within the blank worked and distended the metal, in cooperation with rollers disposed externally of the blank, to form bulges in the blank which were then collapsed by axial pressure to form the groove walls.
Each groove in this latter process was formed separately and the mandrels were retracted away from the pulley after each groove was formed in order to be positioned for formation of the next groove. In this process working and thinning of the metal could be minimized, but not eliminated, by collapsing the blank axially as the interior rollers or segments expanded to form the bulge. The interior rollers or segments were retracted before the bulge was collapsed to form the wall of the pulley groove. Usually both the rollers and the blank were rotated.
Still another prior art process is to split a round, flat blank having a thick edge by forcing a circular rotating tool into the edge intermediate the thickness of the blank to form a single groove pulley. Multigroove pulleys were built up by welding alternate spacers and similarly formed single groove structures together.
Both of these last two processes have also proved quite inefficient and expensive, including tooling costs, in actual use and require a great many steps, as well as expensive mandrels and equipment in addition to the presses. Both, also fail to obtain the object of a satisfactory sheet metal pulley which is both uniform in concentricity, runout and balance relative to other pulleys made in the same way and economically and technically feasible for mass production.